<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>

      fieldset{
          width: 300px;
          height: 300px;
      }

    </style>
</head>
<body>
   
      <form action="">

        <fieldset>
            <legend>用户登录:</legend>
            用户名: <input type="text" />
            <br>
            密&nbsp;&nbsp;&nbsp;码: <input type="password" />
          </fieldset>

      </form>
    
</body>
</html>